1. Field of the Invention
The present invention relates to an engine control apparatus for controlling ignition timing and/or fuel injection timing, and more particularly to an engine control apparatus capable of accurately and promptly discriminating cylinders.
2. Description of the Prior Art
In the fields of engine control, there have been conventionally known various cylinder discriminating techniques. In such cylinder discriminating techniques, a crank angle is generally detected by a rotational sensor such as a Hall sensor or an optical sensor which generates a crank angle signal having a plurality of signal levels. A cam angle is also detected by the similar sensor, so as to be used together with the crank angle for discriminating cylinders of an engine.
One example of discriminating cylinders on the basis of these crank angle and cam angle signals is, for example, disclosed in the Unexamined Japanese Patent Application No. 3-172558/1991.
FIG. 4 illustrates the principle of the discriminating method in accordance with the teaching of the Unexamined Japanese Patent Application No. 3-172558/1991. A crank angle rotor is generally formed with numerous projections and recessions alternately disposed at the circumferential peripheral portion thereof so as to generate a pulsation signal. The circumferential peripheral portion of the crank angle rotor used in this prior art is further provided with a plurality of silent sections having no projections therein being disposed at predetermined intervals.
In FIG. 4, a crank angle sensor signal (a) has a plurality of non-pulsation components as generally denoted by a reference character (c). Reference positions (REF) are detected on the basis of these non-pulsation components (c). On the other hand, a cam angle rotor has a plurality of projections having different widths in connection with the total number of cylinders. Thus, a cam angle sensor signal (b) generates a plurality of HIGH-level sections each having a width (d). The number of these HIGH-level sections is the same as the number of cylinders. The width (d) is differentiated from each other among HIGH-level sections so that each of the cylinders can be discriminated based on the detection of pulse counts of the crank angle signal encompassed during the width (d).
Another example of discriminating cylinders on the basis of the crank angle and cam angle signals is disclosed in the Unexamined Japanese Patent Application No. 60-138251/1985.
FIG. 5 illustrates the principle of the discriminating method in accordance with the teaching of the Unexamined Japanese Patent Application No. 60-138251/1985. As shown in FIG. 5, a crank angle sensor signal alternates at regular intervals. On the other hand, a cam angle sensor signal alternates at irregular intervals. The level of the cam angle signal is detected at two points corresponding to a rise timing A and a drop timing B of the crank angle sensor signal as shown in FIG. 5. Through this detection, four signal patterns of HIGH-HIGH, HIGH-LOW, LOW-HIGH, and LOW-LOW are detected. The cylinder discrimination is then carried out on the basis of thus obtained four patterns of HIGH-HIGH, HIGH-LOW, LOW-HIGH, and LOW-LOW as shown FIG. 6.
These conventional discriminating methods are, however, disadvantageous in the following point when used in a distributorless ignition system. A major problem is that these discrimination methods cannot be applied to 8-cylinder engines. First of all, the system disclosed in the Unexamined Japanese Patent Application No. 3-172558/1991 will require to excessively enlarge the crank rotor radius. Because, the cam angle rotor needs to be formed with eight projections having mutually different widths so as to encompass 1 to 8 crank angle signal pulses therein, respectively. Secondly, the system disclosed in the Unexamined Japanese Patent Application No. 60-138251/1985 will provide only four signal patterns using HIGH and LOW-levels at best. Consequently, an additional rotation sensor will be inevitably required in the case where an ignition coil is provided per cylinder in an 8-cylinder engine.